The background description provided here is presents the context of the disclosure generally. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to perform etching and/or other treatment of substrates such as semiconductor wafers. A substrate may be arranged on a pedestal in a processing chamber of the substrate processing system. For example, during etching in a plasma etcher, a gas mixture including one or more precursors is introduced into the processing chamber and plasma is struck to etch the substrate.
It is useful to monitor conditions inside a semiconductor processing chamber, so that processes can be optimized. Conditions inside the chamber may indicate a need for cleaning, for example, or may indicate whether the chamber is sufficiently “seasoned” to be in an optimal condition for wafer fabrication. In one aspect, “seasoning” may refer to a condition of the chamber at a particular time, or it may refer to a steady state condition of the chamber.
It is known to monitor chamber conditions using apparatus positioned outside the chamber. Conditions inside a semiconductor processing chamber are quite hostile to many kinds of equipment. Observation of chamber conditions may be performed through one or more windows in the chamber. It is known, for example, to position a camera or other sensing device at one of the windows to observe conditions inside the chamber.
FIG. 1 shows an example of a substrate processing chamber 500 for performing etching using RF plasma is shown. The substrate processing chamber 500 includes a processing chamber 502 that encloses other components of the substrate processing chamber 500 and contains the RF plasma. The substrate processing chamber 500 includes an upper electrode 504 and a pedestal 506 including a lower electrode 507. An edge coupling ring 503 is supported by the pedestal 506 and is arranged around the substrate 508. One or more actuators 505 may be used to move the edge coupling ring 503. During operation, a substrate 508 is arranged on the pedestal 506 between the upper electrode 504 and the lower electrode 507.
For example only, the upper electrode 504 may include a showerhead 509 that introduces and distributes process gases. The showerhead 509 may include a stem portion including one end connected to a top surface of the processing chamber. A base portion is generally cylindrical and extends radially outwardly from an opposite end of the stem portion at a location that is spaced from the top surface of the processing chamber. A substrate-facing surface or faceplate of the base portion of the showerhead includes a plurality of holes through which process gas or purge gas flows. Alternately, the upper electrode 504 may include a conducting plate and the process gases may be introduced in another manner. The lower electrode 507 may be arranged in a non-conductive pedestal. Alternately, the pedestal 506 may include an electrostatic chuck that includes a conductive plate that acts as the lower electrode 507.
An RF generating system 510 generates and outputs an RF voltage to one of the upper electrode 504 and the lower electrode 507. The other one of the upper electrode 504 and the lower electrode 507 may be DC grounded, AC grounded or floating. For example only, the RF generating system 510 may include an RF voltage generator 511 that generates the RF voltage that is fed by a matching and distribution network 512 to the upper electrode 504 or the lower electrode 507. In other examples, the plasma may be generated inductively or remotely.
A gas delivery system 530 includes one or more gas sources 532-1, 532-2, . . . , and 532-N (collectively gas sources 532), where N is an integer greater than zero. The gas sources supply one or more precursors and mixtures thereof. The gas sources may also supply purge gas. Vaporized precursor may also be used. The gas sources 532 are connected by valves 534-1, 534-2, . . . , and 534-N (collectively valves 534) and mass flow controllers 536-1, 536-2, . . . , and 536-N (collectively mass flow controllers 536) to a manifold 540. An output of the manifold 540 is fed to the processing chamber 502. For example only, the output of the manifold 540 is fed to the showerhead 509.
A heater 542 may be connected to a heater coil (not shown) arranged in the pedestal 506. The heater 542 may be used to control a temperature of the pedestal 506 and the substrate 508. A valve 550 and pump 552 may be used to evacuate reactants from the processing chamber 502. A controller 560 may be used to control components of the substrate processing chamber 500. The controller 560 may also be used to control the actuator 505 to adjust a position of one or more portions of the edge coupling ring 503.
A robot 570 and a sensor 572 may be used to measure erosion of the edge coupling ring. In some examples, the sensor 572 may include a depth gauge. The robot 570 may move the depth gauge in contact with the edge coupling ring to measure erosion. Alternately, a laser interferometer (with or without the robot 570) may be used to measure erosion without direct contact. The robot 570 may be omitted if the laser interferometer can be positioned with a direct line of sight to the edge coupling ring.
FIG. 2A shows an example of an approach to detecting conditions at a wall of a chamber. For ease of description, many of the elements in FIG. 1 are omitted here. In FIG. 2A, a semiconductor processing chamber 100 includes a pedestal 110, on which an electrostatic chuck (ESC) 115 may be mounted. A wafer or substrate 120 is positioned on the ESC.
At the top of the chamber, a conduit 130 passes plasma to showerhead 135, which distributes the plasma in the chamber. As substrates get processed, there can be buildup on the walls of the chamber. A detection apparatus includes a light source 170 and a camera/detector 175. The light source 170 shines light through a first opening 180 onto a mirror 165 at an opposite end of the chamber. Camera/detector 175 picks up light reflected from mirror 165 through a second opening 185. Controller 160 communicates with camera/detector 175 to operate the camera and to receive output from the camera/detector. Controller 160 also controls operation of light source 170. Shutters 190, 195 respectively operate to cover windows 180, 185 when the detection apparatus is not in operation, or the chamber is not in use.
Controller 160 may process data from the camera/detector 175, using known signal processing algorithms and/or other computational techniques, to obtain information about wall conditions in chamber 100. Alternatively, controller 160 may pass obtained data to other processing apparatus (not shown here for ease of description) for that purpose.
In operation, whatever builds up on the chamber walls also builds up on mirror 165, thereby affecting the mirror's ability to reflect light from source 170 to camera/detector 175. Controller 160 takes the amount of light that camera/detector 175 receives as reflected from mirror 165, and given the light that light source 170 outputs, and the material being deposited on the walls of the chamber (and therefore on the mirror 165), computes/estimates the amount of buildup on the mirror.
There also will be buildup on the windows 180, 185 through which the transmitted light enters, and the reflected light leaves. As an approximation, to make calculations easier it may be assumed that the amount of buildup on the windows is the same as the amount of buildup on the mirror.
FIG. 2B shows a variant of the setup in FIG. 2A, in which the camera/detector 175 and the window 185 are positioned on an opposite side of the chamber from their positions in the system of FIG. 2A. The FIG. 2B approach removes the requirement for a mirror inside chamber 100. Again, as an approximation, for ease of calculation, it may be assumed that the amount of buildup on window 185 will be the same as on window 180.
There are various issues associated with the FIG. 2A apparatus and detection approach. One issue with respect to the FIG. 2A system is that the light from source 170 has to be tightly focused onto mirror 165, so that what comes back from mirror 165 is a reliable indication of the light that the source 170 is providing. The light source 170 may be a laser or other source of coherent light which enables tight focusing on mirror 165. Movement of any of several elements in FIG. 2 can affect the ability of camera/detector 175 to receive reflected light properly. For example, movement of the light source 170 outside the chamber, or movement of the mirror 165 inside the chamber, or movement of the chamber itself may require refocusing of the light source 170 onto the mirror 165. In addition, movement of the mirror 165 or chamber containing the mirror may require repositioning of the camera/detector 175, as the angle of reflection from the mirror 165 may change. As a result of all of these possibilities, frequent repositioning/refocusing of source 170 and/or camera/detector 175 may be necessary. Another issue is that, just as there is buildup on mirror 165, there also will be buildup on windows 180, 185, thereby affecting not only the amount of light that the source 170 will provide, but also the amount that camera/detector 175 will detect. While it may be assumed that buildup of material on chamber walls (and hence on the mirror and windows) is uniform, depending on the process being utilized, that might not be the case. As a result, given the different location of the mirror 165 from the windows 180, 185, there may be different amounts of buildup in the different locations, making it difficult to provide a reliable estimate of buildup on the windows.
The FIG. 2B approach eliminates detection and accuracy issues associated with the mirror 165. However, because the windows 180, 185 are on opposite sides of the chamber, the FIG. 2B approach retains the issue of differential amounts of buildup in different parts of the chamber. In addition, by using direct transmission of light instead of reflected transmission, the FIG. 2B approach ameliorates focusing issues associated with movement of light source 170, camera/detector 175, or the chamber 100. However, those focusing issues will persist to some degree.
There have been efforts to provide detection equipment inside the chamber, to provide more direct measurement. A significant difficulty with that approach is the hostile environment that plasma provides to that equipment.
It would be useful to have more accurate monitoring of chamber conditions.